In the conventional cheese making process for making cheddar, colby, or other similar types of cheese, milk is introduced into the cheese making vat along with rennet and a starter. After the materials have been thoroughly blended or mixed, the agitation is stopped which results in the coagulation or gelling of the curd. When the product reaches a given consistency, the curd is then cut into cubes by use of cutter blades. The curds are then slowly stirred by agitator blades or baffles while cooking to firm up the curd and draw out the whey.
In the past cheese making has been normally carried out in large open-top vats. Open-top vats are not a sanitary design, for it is possible that foreign material can fall into the vat, and contamination such as bacteriaphage is possible. As a further disadvantage, when the product is heated in an open top vat, drying can occur on the walls of the vat, and the dried residue must be manually scrubbed from the vat after the cheese making operation. The scrubbing is an abrasive action which tends to roughen the interior surface of the vat, thereby increasing the tendency for the product to adhere to the vat surface.
Because of the problems encountered with the open-top vat, there has recently been increased activity in closed cheese making vats. Vertical cheese making vats, such as that disclosed in U.S. Pat. No. 3,541,687, provide a more sanitary design which decreases contamination. As a further advantage, the closed vat reduces the necessary floor space and permits maximum use of automatic controls and thereby results in better control of product quality.
While the conventional closed vat provides a more sanitary design that an open-top vat, the conventional closed vat is not sealed to the atmosphere during the entire cheese making operation, for it normally is necessary to insert and remove various types of implements, such as baffles, agitators, cutters, and the like which periodically expose the product to the atmosphere.